Surgical guidance enables surgeons to localize the position of surgical instruments relative to the human body without having complete visual access during surgery. Surgical guidance is routinely used in surgeries that involve anatomical locations such as the spine, brain, hip or other organs.
In general, surgical guidance consists of two steps: The first step includes the acquisition of a three dimensional (3D) data set of a relevant anatomical region of the body. This step may involve single or multiple imaging modalities such as computed tomography (CT), magnetic resonance tomography (MRT), positron emission tomography (PET) and ultrasound (US). The 3D data set may be acquired before and/or during the surgical procedure. In the second step, the spatial position of the body and the spatial relation of the surgical instruments to the position of the anatomical region are tracked during the surgery. The spatial position of this anatomical region is then mapped to its 3D data set using specific image registration techniques. After registration, the spatial position of the surgical instruments as they are being used by the surgeon can be displayed relative to the previously acquired 3D data set of the anatomical region. Surgical guidance systems usually incorporate the use of a reference structure which is affixed to the patient in order to track patient motion and breathing so that tool tracking remains accurate during the procedure.
In some applications, optical-based systems are used for tracking spatial positions of tools and the reference frame during the surgery. These systems are based on two cameras that detect the positions of at least three markers attached to the tracked surgical instruments and require line-of-sight from the cameras to the markers (for example, mounted with LEDs, or mounted with reflective probes). This necessitates the careful positioning of the cameras and design of tracked instruments so that line-of-sight is maintained during a surgical procedure.